Oral care products such as dentifrice and mouthrinse are routinely used by consumers as part of their oral care hygiene regimens. It is well known that oral care products can provide both therapeutic and cosmetic hygiene benefits to consumers. Therapeutic benefits include caries prevention which is typically delivered through the use of various fluoride salts; gingivitis prevention by the use of an antimicrobial agent such as triclosan, stannous fluoride, or essential oils; or hypersensitivity control through the use of ingredients such as strontium chloride or potassium nitrate. Cosmetic benefits provided by oral care products include the control of plaque and calculus formation, removal and prevention of tooth stain, tooth whitening, breath freshening, and overall improvements in mouth feel impression which can be broadly characterized as mouth feel aesthetics. Calculus and plaque along with behavioral and environmental factors lead to formation of dental stains, significantly affecting the aesthetic appearance of teeth. Behavioral and environmental factors that contribute to teeth staining propensity include regular use of coffee, tea, cola or tobacco products, and also the use of certain oral products containing ingredients that promote staining, such as cationic antimicrobials and metal salts.
Thus daily oral care at home requires products with multiple ingredients working by different mechanisms to provide the complete range of therapeutic and aesthetic benefits, including anticaries, antimicrobial, antigingivitis, antiplaque and anticalculus as well as antiodor, mouth refreshment, stain removal, stain control and tooth whitening. In order for oral care products for daily use such as dentifrice and rinses to provide complete oral care it is necessary to combine actives and additives, many of which have the disadvantage of causing negative aesthetics during use, in particular unpleasant taste and sensations and stain promotion. The unpleasant taste and mouth sensations have been described as having one or more of bitter, metallic, astringent, salty, numbing, stinging, burning, prickling, and even irritating aspects. Typical ingredients for oral care use that are associated with these aesthetic negatives include antimicrobial agents such as cetyl pyridinium chloride, chlorhexidine, stannous, copper and zinc salts; tooth bleaching agents such as peroxides; antitartar agents such as pyrophosphate, tripolyphosphate and hexametaphosphate; and excipients such as baking soda and surfactants. To mitigate the aesthetic negatives from these ingredients, oral care products are typically formulated with flavoring agents and sweeteners to taste as good as possible and be consumer acceptable.
Because of the many proven benefits to the oral cavity, stannous ions are desired to be incorporated in oral care compositions. Stannous ions, typically supplied from stannous fluoride in oral care compositions are used to provide benefits including antimicrobial, anti-plaque, antigingivitis and anti-sensitivity and to prevent mouth malodor. However, formulating with stannous ions has proven to be challenging as formulations containing the stannous ions have been known to not be aesthetically pleasing. In addition, it has been found that certain flavoring oils, especially mint-type oils when used in combination with stannous ions can exhibit instability and malodor production.
Refining or further processing of natural flavor oils following extraction from plants or plant materials, to improve quality and stability have been described in the art. Generally these processing methods are aimed at removing or reducing the content in the oils of components believed to be responsible for instability or undesirable taste or odor characteristics. For example, flavor oils have been treated to remove or reduce the content of terpenes, menthofuran, pulegone and dimethyl sulfide. Such treatment processes are described for example in U.S. Pat. Nos. 3,867,262; 4,440,790; 4,613,513; 4,708,880; 4,844,883; 4,816,616; 4,948,595; 5,116,625; 5,128,154; 5,204,128; 5,298,238; 5,425,962; and 6,479,088, and include distillation, nitrogen sparging, and chemical treatment to oxidize or inactivate such undesirable components.
Peppermint oils for example may be distilled to remove or reduce the level of dimethyl sulfide which is reported to provide an undesirable green weedy note. Steam or vacuum distillations have been performed to refine peppermint oil. However, such distillation processes are not entirely satisfactory. The typical steam distillation process in addition to removing dimethyl sulfide also removes other low boiling point peppermint oil components. It is therefore necessary when refining peppermint oil to separate desirable low boiling components from the distillate and add them back at least in part to the flavor. This increases the cost and time of the distillation process. An additional problem with most currently used methods of refining peppermint oil is that they may subject the peppermint oil to extreme conditions, such as excessive heat. This can produce undesirable changes in the flavor.
There continues to be a need for improved processing of flavor oils to provide optimum taste and odor characteristics and stability, in particular to remove malodor-forming components specifically dimethyl sulfoxide, which has now been found to be the major form of malodor-precursor sulfur species in flavor oils. The present invention accordingly involves the removal of such previously unrecognized undesirable odor-forming components from starting flavor oil(s) with production of a stable flavor which is essentially free of undesirable amounts of such malodor-forming components and hence also free of malodor-forming or flavor contaminating tendencies due to reactions with reducing agents such as stannous in oral care compositions.